ok, lol, but seeing as I don't have a spare (or portable) heat pump, a small electric heater makes sense. However, mine is 1500W, which will exceed the single battery max draw of 100A.
Itenerant, the inverter charger is a Samlex 3012, it does seem to have pass-through capability.
On further reading manual does make mention of a stand-by mode which states:
3.4 STANDBY MODE
When in Standby Mode, the EVO will stop inverting or passing through AC input to AC output.
Also, charging is cancelled when in Standby Mode.
A short press (0.1 seconds) of the ON/OFF Button will change the operational mode from
Inverting or Charging Mode to Standby Mode. A subsequent short press when in Standby
Mode will return the EVO Inverter Charger to Inverting or Charging Mode.
This mode is used for uploading firmware for EVO Inverter Charger through the SD Card.
This mode may also be used to temporarily halt inverting, charging and AC pass through.
So I guess I can use this to limit charging, will have to check to make sure stand-by mode does not disrupt 12V, which I would doubt.